1) I sent her two emails last week, but he hasn't replied to any of them. (I think both the simple past and the past perfect are acceptable).
2) How long does it take him to drive to wrok?
3) Why was she hurrying to school?
How often haver they been to Japan?
Who has asked a very difficult question?
4) How long did she live in Paris?
Who did you phone last night?
5) Where did your friends spend their holiday last summer?
How much did he pay for that shirt?
6) How much did he spend on that shirt?
I will have to leave Turin by six o'clock tomorrow.
Also: I must leave Turin by six o'clock tomorrow.